{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

mbmb451b_glycogenmet - Glycogen Metabolism Glycogen...

Info iconThis preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon
Glycogen Metabolism Glycogen Breakdown Glycogen Synthesis Control of Glycogen Metabolism Glycogen Storage Diseases
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Glycogen Glycogen - animal storage glucan 100- to 400-Å-diameter cytosolic granules up to 120,000 glucose units α (1 6) branches every 8 to 12 residues muscle has 1-2% (max) by weight liver has 10% (max) by weight ~12 hour supply Although metabolism of fat provides more energy: 1. Muscle mobilize glycogen faster than fat 2. Fatty acids of fat cannot be metabolized anaerobically 3. Animals cannot convert fatty acid to glucose (glycerol can be converted to glucose)
Background image of page 2
Glycogen Breakdown Three enzymes: glycogen phosphorylase glycogen debranching enzyme phosphoglucomutase Glycogen phosphorylase ( phosphorylase ) - phosphorolysis of glucose residues at least 5 units from branch point Glycogen + P i glycogen + glucose-1-phosphate (n residues) (n-1 residues) homodimer of 842-residues (92-kD) subunits allosteric regulation - inhibitors (ATP, glucose-6- phosphate, glucose) and activator (AMP), T R covalent modification (phosphorylation) - modification/demodification phosphorylase a ( active , SerOPO 3 2- ) phosphorylase b ( less active , Ser) narrow 30-Å crevice binds glycogen, accommodates 4 to 5 residues Pyridoxal-5-phosphate (vit B 6 derivative) cofactor - located near active site, general acid-base catalyst Rapid equilibrium Random Bi Bi kinetics
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Glycogen Breakdown Glycogen debranching enzyme - possesses two activities α (1 4) transglycosylase (glycosyl transferase) 90% glycogen glucose-1-phosphate transfers trisaccharide unit from "limit branch" to nonreducing end of another branch α (1 6) glucosidase 10% glycogen glucose Debranching activity < phosphorylase activity
Background image of page 4
Glycogen Breakdown Phosphoglucomutase - a phosphoenzyme (Ser) reaction similar to that of phosphoglycerate mutase formation of glucose-1,6-bisphosphate (required for full activity) phosphoglucokinase - provides product glucose-1-phosphate + ATP glucose-1,6-bisphosphate
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Glycogen Breakdown Thermodynamic considerations phosphorylase reaction: G˚' = +3.1 kJ . mol -1 G = 0 when [P i /glucose-1-phosphate] = 3.5 under physiological conditions [P i /glucose-1-phosphate] ~ 30 to 100 G˚' = -5 to -8 kJ . mol -1 Glycogen breakdown is exergonic (favorable) Glycogen synthesis must occur by a separate pathway
Background image of page 6
Glycogen Synthesis Three enzymes: UDP-glucose pyrophosphorylase glycogen synthase
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 8
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}